Cognitive web services are widely used on the web for providing artificial intelligence (AI) capabilities. These web services provide a variety of features, including text and natural language understanding capabilities, chatbots, speech translation, speech-to-text and text-to-speech conversion, visual recognition, image and video recognition, machine learning capabilities, and other advanced capabilities. These services have proliferated in recent years with new features and types of services constantly being added. These cognitive services open up a wide range of capabilities for software applications. Users have access to state-of-the-art AI capabilities without having the need to install and run the software on their own systems. Cognitive web services present challenges as well. The web services need to be scalable to handle a large number of users. High availability is critically important. Data privacy can be a significant issue. The programming model and application program interface (API) need to be properly designed so that the services are both versatile and easy to use. This special issue seeks papers in all areas related to cognitive web services for machine learning and data analytics. Topics of interest include, but are not limited to: New types of web services for machine learning and data analytics Architectural design of web services for machine learning and data analytics Scalability and performance issues Performance modelling and optimization of web services for machine learning and data analytics Data privacy issues for cognitive web services Programming model and API design issues Machine learning web services operation and life cycle management Machine learning model management issues Empirical evaluations and comparisons of cognitive web services Algorithms and tools for selecting the best cognitive web services Cognitive web service pricing and incentives Testbeds and simulation platforms of web services for machine learning and data analytics Innovative applications using cognitive web services Experiences gained from deploying large-scale cognitive web services Important Dates Paper submissions due: 1 February 2021 First-round review due: 1 April 2021 Revision due: 7 May 2021 Final decision notification: 25 May 2021 Camera-ready submission due: 30 June 2021 Publication: September/October 2021